A whole new regime of science and applications is opened by the ability to switch nanophotonic structures very quickly while light propagates through them. This will allow the catching or releasing of photons, or changing the frequency and bandwidth of confined photons, all of which are essential to applications in active photonic integrated circuits.

Therefore, we have demonstrated the first high-speed all-optical switching of semiconductor microcavities made of GaAs-AlAs. We have “zapped” the cavities with an ultrashort fs laser pulse that shifted the cavity resonance to a higher frequency in a few ps, and the switched state relaxed with a time constant of 50 ps.

Figure 1: Cavity resonance frequency and refractive index change versus time delay Δt. The cavity resonance frequency is switched with two trigger pulses separated by δt_tr = 1.0 ps and two probe pulses separated by (a) δt_pr = 3.0 ps and (b) δt_pr = 2.0 ps. Horizontal dashed lines are the unswitched resonance. Solid curves are the calculated resonance frequency and the dotted lines show the refractive index change in the dynamic model. Blue-filled regions indicate the overlap of the first trigger pulse with probe pulses and yellow regions indicate the overlap of the second trigger pulse with the probe pulses. From E. Yuce, G. Ctistis, J. Claudon, E. Dupuy, R.D. Buijs, B. de Ronde, A. P. Mosk, J.-M. Gerard, and W.L. Vos, Opt. Lett. 38, 374 (2013), click here.

Recently, we have managed to switch cavity resonances by means of the near-instantaneous electronic Kerr effect. As a result, a whole on-off switching event is only limited by the speed of light, and completed within less than 1 picosecond. We have used these features to repeatedly switch a microcavity, see Figure 1. This observation corresponds to single-channel switch speeds in excess of 1 THz, more than 100x faster than the switch speed in a modern computer!

Earlier, we have observed that curious phenomenon the frequency of light trapped inside a switched cavity can be red-shifted much more than the shift of the cavity resonance; hence the frequency change is not-adiabatic with the cavity, see Figure 2. We are currently busy to understand the physics behind this phenomenon.

Figure 2: Transient reflectivity of a photonic microcavity that is subjected to an ultrafast all-optical switching pulse. It is seen that the cavity resonance (a region of low reflectivity) moves upward by 10 meV a few picoseconds after the switching pulse, after which it returns to its normal value in about 50 ps. Surprisingly, the transient reflectivity below the switched resonance frequency can exceed unity, a clear indication that light is frequency-converted effciently in our microcavity. [P.J. Harding, H.J. Bakker, A. Hartsuiker, J. Claudon, A.P. Mosk, J.-M. Gérard, and W.L. Vos, J. Opt. Soc. Am. B 29, A1-A5 (2012), click here].